North Korea is flouting UN sanctions by exporting coal, iron, steel and other commodities banned under UN sanctions, earning nearly $200 million in revenue last year, a UN report says.

The UN Security Council has unanimously imposed new sanctions on North Korea, slapping a ban on textile exports and restricting shipments of oil products to punish Pyongyang for its sixth and largest nuclear test.

South Korea's foreign minister says that North Korea's nuclear capability is expanding fast, echoing alarm around the world over the isolated state's fifth nuclear test carried out in defiance of UN sanctions.